LITHOPROBE - NEW PERSPECTIVES ON CRUSTAL EVOLUTION

被引:76
作者
CLOWES, RM
COOK, FA
GREEN, AG
KEEN, CE
LUDDEN, JN
PERCIVAL, JA
QUINLAN, GM
WEST, GF
机构
[1] UNIV CALGARY, DEPT GEOL & GEOPHYS, CALGARY T2N 1N4, ALBERTA, CANADA
[2] GEOL SURVEY CANADA, DIV CONTINENTAL GEOSCI, OTTAWA K1A 0Y3, ON, CANADA
[3] GEOL SURVEY CANADA, BEDFORD INST OCEANOG, ATLANTIC GEOSCI CTR, DARTMOUTH B2Y 4A2, NS, CANADA
[4] UNIV MONTREAL, DEPT GEOL, MONTREAL H3C 3J7, QUEBEC, CANADA
[5] GEOL SURVEY CANADA, DIV CONTINENTAL GEOSCI, OTTAWA K1A 0E8, ONTARIO, CANADA
[6] MEM UNIV NEWFOUNDLAND, DEPT EARTH SCI, ST JOHNS A1B 3X5, NEWFOUNDLAND, CANADA
[7] UNIV TORONTO, DEPT PHYS, DIV GEOPHYS, TORONTO M5S 1A7, ONTARIO, CANADA
[8] UNIV BRITISH COLUMBIA, CTR GEOL SCI, DEPT GEOPHYS & ASTRON, VANCOUVER V6T 1Z4, BC, CANADA
关键词
D O I
10.1139/e92-145
中图分类号
P [天文学、地球科学];
学科分类号
07 ;
摘要
Lithoprobe is Canada's national, collaborative, multidisciplinary earth science research program directed toward an enhanced understanding of how the North American continent evolved. Research in its eight transects or study areas, which span the country from Vancouver Island to Newfoundland and geological time from 4 Ga to the present, is spearheaded by seismic reflection surveys. These, combined with many other studies, are providing new insight into the varied tectonic processes that have been active in forming the continent. Results from the Southern Cordillera transect show that Mesozoic crustal growth occurred in the central and eastern Cordillera by the accretion and amalgamation of exotic terranes, the collision of which resulted in the generation of crustal-scale antiforms and duplexes. After the principal periods of compression, this area was affected by a major episode of extension that led to the unroofing of the metamorphic core complexes. Farther to the west, past and present subduction processes have eroded the lower lithosphere of accreted terranes and left underplated sediments and oceanic lithosphere. The Lithoprobe East transect, covering the Paleozoic Newfoundland Appalachians and Mesozoic rifted Atlantic margin, reveals three lower crustal blocks, each with distinctive reflection signatures on marine seismic data. Structures of the geologically established tectono-stratigraphic domains, imaged clearly by new onshore reflection data, sole at upper crustal to mid-crustal levels, suggesting that much of the surface stratigraphy is allochthonous to the lower crustal blocks. At the ocean-continent transition, interpretations suggest underplating of thinned continental crust by basaltic melt during the rifting process. In Lake Superior, data from the Great Lakes International Multidisciplinary Program on Crustal Evolution (GLIMPCE) transect reveal the complex structures of the late Middle Proterozoic Keweenawan rift, which is up to 35 km deep, that almost split North America. The GLIMPCE data in Lake Huron show a spectacular series of east-dipping crustal-scale reflections that coincide with the Grenville front tectonic zone. These and other data have led to a two-stage model involving collision of an exotic terrane with the southern Superior cratonic margin in the late Early Proterozoic followed by stacking-crustal penetrating imbrication and ramping associated with the Middle Proterozoic Grenvillian orogeny. The Archean Kapuskasing structural zone, a prominent northeast-trending feature that cuts obliquely across the dominant east-west structures of the Superior Province, is interpreted as a thin thrust sheet, soled by a variably reflective decollement, above which about 70 km of crustal shortening has occurred to bring mid-crustal to lower crustal rocks to the surface, and below which the Moho deepens. The shortening may have been accomplished by brittle faulting and erosion at levels above 20 km and ductile folding or faulting in the lower crust. Preliminary studies in the Archean Abitibi greenstone belt indicate that two major fault zones, the Larder Lake - Cadillac and Porcupine-Destor, which host significant mineralization, were generated by crustal-scale thrust and (or) strike-slip tectonics. Archean crustal sections are as structurally diverse and complex as their Proterozoic and Phanerozoic counterparts. The reflection Moho has highly variable characteristics as imaged within transects and among different transects. Crustal and Moho reflectivity observed in the various transects is caused by a wide range of features, including fault-shear zones, lithologic contacts, compositional layering, fluids in zones of high porosity, and anisotropy.
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收藏
页码:1813 / 1864
页数:52
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